✓ Revise Right course
Power is the rate at which energy is transferred or the rate at which work is done, measured in watts (W). Free GCSE Physics notes and 14 FAQs.
Understanding Power is part of Energy changes in a system, and the ways energy is stored before and after such changes in GCSE AQA Higher Physics.
4 min
Reading time
14
Lessons in this topic
GCSE AQA Higher
Pathway
Reviewed by Revise Right
Content review
Power is the rate at which energy is transferred or the rate at which work is done, measured in watts (W). Free GCSE Physics notes and 14 FAQs.
AQA GCSE Physics mock draft, 26–31 Oct. Draft coverage: Physics Paper 1 (Higher tier). Reviewed for an original-practice sitting; check student availability before registering. Marking and results will follow later, after separate approval. Eligible new accounts receive a five-day Pro trial when signup email verification completes. Previous trials keep their original expiry. After expiry, new papers need Pro unless you have an explicitly confirmed free sitting offer for this event. That offer adds no Pro time or AI learning. Saved attempts and released results remain readable. No card or automatic charge.
Use this lesson to stay inside Energy changes in a system, and the ways energy is stored before and after such changes while connecting the detail back to the wider Energy topic.
Read the core explanations from Understanding Power before testing yourself from memory.
Two identical cars race up the same hill. Both use the same amount of fuel energy. But one takes 10 seconds, the other takes 20 seconds. Which engine is more powerful?
The faster car has the more powerful engine. Power isn't about how much energy you use — it's about how quickly you use it. This is the key insight that unlocks everything about power in physics.
Notice the word 'rate' - it means how much of something happens in a given time. For power, that time is measured in seconds, so watts tell you how many joules are transferred each second. When energy transfers quickly, power is high. When energy transfers slowly, power is low.
This definition is crucial for calculations. If a device transfers 100 J of energy in 10 seconds, its power is 100 ÷ 10 = 10 W. The energy transfer of 1 joule per second equals exactly 1 watt of power.
Both formulas give the same result because work done equals energy transferred. Use whichever matches the information given in the question. Remember: power is always energy (or work) divided by time, never the other way around.
Let's see how power calculations work in exam-style questions. Pay attention to the units and the step-by-step method that gets you full marks.
Worked example: Calculating Motor Power
An electric motor lifts a 50 kg box through a height of 3 m in 5 seconds. Calculate the power of the motor. (g = 10 N/kg) [4 marks]
Answer: 300 W
Notice how we broke this down into clear steps. The examiner awards method marks for each stage, so show your working even if you're confident with the calculation.
Worked example: Comparing Power Ratings
Two motors both lift the same 20 kg mass through 2 m. Motor A takes 4 seconds, Motor B takes 8 seconds. Which motor is more powerful and by how much? (g = 10 N/kg)
Answer: Motor A is more powerful (100 W vs 50 W). Motor A has twice the power of Motor B.
Understanding power helps explain why some devices are more impressive than others, even when they use the same total energy. Here's where the definition really comes alive.
Consider two electric motors that both lift the same weight through the same height. They both do exactly the same amount of work (same energy transfer). But if one motor does it in 2 seconds and the other takes 10 seconds, the first motor has 5 times more power.
This is why a sports car engine (high power) can accelerate quickly, while a small car engine (lower power) takes longer to reach the same speed. Both might use similar amounts of fuel energy over a journey, but the sports car transfers that energy much more rapidly.
Exam Insight: Questions often ask you to compare devices with the same energy transfer but different times. The key is recognising that power = energy ÷ time, so shorter time means higher power.
Power questions follow predictable patterns in GCSE exams. Master these techniques and you'll recognise the question types instantly.
Command Word Alert: 'Calculate' questions need working shown. 'Compare' questions need you to work out both values and state the difference. 'Explain' questions need you to link power to the rate of energy transfer.
Common Exam Trap: Questions might give you energy in kJ (kilojoules). Remember to convert: 1 kJ = 1000 J. If you forget this conversion, your power will be 1000 times too small.
A high-power device is not automatically more efficient. Power tells you the rate of energy transfer, whereas efficiency tells you what fraction of the input becomes useful output. A powerful machine can still waste a large fraction of its energy. Keeping these ideas separate helps with comparison questions.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
One watt equals one joule of energy transferred per second (1 W = 1 J/s). So if a device transfers 100 J of energy in 10 seconds, its power is 100 ÷ 10 = 10 W.
Power is measured in watts (W). One watt equals one joule of energy transferred per second, so 1 W = 1 J/s, and the number of watts gives how many joules are transferred each second.
Power is the rate at which energy is transferred or the rate at which work is done, measured in watts (W). When energy transfers quickly, power is high; when energy transfers slowly, power is low. Power is about how quickly energy is used, not how much.
Power using work done is P = W/t, where P is power in watts, W is work done in joules and t is time in seconds. It gives the same result as P = E/t because work done equals energy transferred.
To find the power of a motor, calculate the weight (mg), then the work done (force × distance), then divide by time. A motor lifting a 50 kg box through 3 m in 5 seconds does 500 × 3 = 1500 J of work, so P = 1500 ÷ 5 = 300 W.
Rate means how much of something happens in a given time. For power, that time is measured in seconds, so power is the amount of energy transferred, or work done, each second. When energy transfers quickly, power is high; when it transfers slowly, power is low.
Power is calculated from energy and time by dividing the energy transferred by the time taken: P = E/t. A device that transfers 100 J of energy in 10 seconds has a power of 100 ÷ 10 = 10 W.
A shorter time means more power because power = energy ÷ time. Two motors lifting the same weight through the same height do the same work, but if one takes 2 seconds and the other 10 seconds, the first motor has 5 times more power.
A more powerful device is not automatically more efficient. Power is the rate of energy transfer, whereas efficiency is the fraction of the input that becomes useful output, so a powerful machine can still waste a large fraction of its energy.
The formulas P = E/t and P = W/t give the same result because work done equals energy transferred. Either one can be used, depending on whether a question gives the energy transferred or the work done, and power is always energy or work divided by time, never the other way around.
The power of two motors is compared by calculating the power of each with P = W/t and stating the difference. Two motors lifting 20 kg through 2 m both do 400 J of work; Motor A takes 4 seconds (100 W) and Motor B takes 8 seconds (50 W), so Motor A is twice as powerful.
A sports car accelerates faster because its engine has a higher power, so it transfers energy much more rapidly. A small car engine with lower power takes longer to reach the same speed, even though both might use similar amounts of fuel energy over a journey.
Kilojoules must be converted to joules in power calculations because P = E/t needs energy in joules to give power in watts, and 1 kJ = 1000 J. If this conversion is missed, the power will be 1000 times too small.
A more powerful machine does not automatically use more energy; it transfers energy more quickly. Two motors lifting the same weight through the same height do the same work, but if one takes 2 seconds and the other 10 seconds, the first has 5 times more power.